Send the following documents with GAS testing form :
1) As per CMR 14 You must be of 20 years of age while applying for the GT. To certify this send matriculation or equivalent certificate(mainly passing certificate) submitted as evidence of age.
2. Lamp handling certificate that you will get from an Underground Mine Manager.
3.Medical certificate obtained not more than one year prior to the date of his application, from a qualified medical practitioner not below the rank of a Civil Assistant Surgeon or from a Certifying Surgeon or from a medical practitioner holding at least a degree in Bachelor of Medicines and Bachelor of Surgery (M.B.B.S.) and registered with Medical Council of India, certifying the candidate to be free from deafness, defective vision or any other infirmity, mental or physical, likely to interfere with the efficiency of his work.
4.A certificate from some person of good repute as to the general good conduct and sobriety of the candidate i.e Character Certificate.
5. Three passport size photograph duly attested by manager.
6. Enclose a self addressed envelope of size 10 cmx22 cm with 25 Rs stamp . (In this envelope they send the GT certificate once you pass the GT Exam)
7. Indian Postal Order of Rs25 in name of Secretary Board Of Mining Examination DGMS Payable at Dhanbad.
After you submit your form make sure that your form has reached DGMS office and do care to enquiry regarding the exam date.Once you pass the GT exam , certificate usually reach in 6-7 months.
Notes and Forms for gas testing Exam can be found in below link.
For Forms Click - http://mineportal.in/study-material-view.php?view=2&topic=39
For Notes Click - http://mineportal.in/study-material-view.php?view=9&topic=33